1. Field of the Invention
The invention relates to a vacuum coating apparatus, and more particularly to a large area roll-to-roll type vacuum coating apparatus.
2. Description of the Prior Art
In the art, roll to roll plasma coating method is a high productivity efficiency technology that is capable of continuously and simultaneously performing multi-layer coatings on flexible substrates. By comparing with the traditional batch or in-line plasma coating process, the roll-to-roll plasma coating technology can significantly reduce the production cost. The flexible substrate for the roll-to-roll type process is mainly made of a soft metal plate, a polymer material, which is light, thin, flexible, elastic, workable and transportable. Therefore, such kind of substrates is widely applied to food packing, capacitors, flexible circuit boards, solar cells, 3C products, heat mirrors and so on.
In particular, the global warming induced by the green house effect has recently become one of crucial issues to nations worldwide. Hence, various renewable energy and energy-saving technologies have been development trends nowadays and are expected to have great contribution to the easing of global warming effect.
For example, the heat mirror can effectively prevent the solar heat from entering the building and allow portions of the visible light to penetrate therethrough, so the energy consumption from the cooling systems and the illumination systems of the building can be greatly reduced. However, market prices for heat mirror glasses, Low-E glasses or flexible heat-insulation films are so high that they have not been adopted economically by the general public. Thus, a technology for providing low-cost heat mirrors is an unavoidable trend.
Generally, a heat mirror is a coating film comprising of at least one metal oxide film, and the corresponding manufacturing process can be a reactive magnetron sputtering process employing a metal target in an oxygen atmosphere. However, the reactive magnetron sputtering process is accompanied by a rapid-change hysteresis phenomenon. Also, the target may suffer from toxicity as well as discharging problem. Hence, the stability of the process speed and the coating rate could not be maintained easily. Though the aforesaid shortcomings may be overcome by introducing dual magnetron targets, OES control and plasma power source, yet the investment involved is comparatively high.
Further, the conventional roll-to-roll type vacuum coating apparatus usually uses a magnetron sputtering source as the plasma source for the coating. While the magnetron sputtering source is at work, the distance between the source and the substrate is about 10 cm and an effective width of about 15 cm hence the plasma is localized within some region, resulting in a local temperature hike on the substrate, causing the deforming of the substrate. Therefore, in the art, a large-capacity cooling cylinder shall be added to the conventional roll-to-roll type vacuum coating apparatus so as to avoid possible over-heating deformation upon the substrate. However, the installation of the cooling cylinder would significantly increase both the facilities cost and the energy consumption. Also, the relative motion between the polymer-made substrate and the cooling cylinder would possibly cause scratches on the substrate.
In addition, the conventional flexible substrate in manufacturing can have a length of several thousand meters. A batch manufacturing process of the conventional roll-to-roll type vacuum coating apparatus usually takes tens of hours to finish. Also, in the manufacturing, the target material for the magnetron sputtering source is consumed with time, and the magnetic field strength on the target surface would increase gradually with the processing time. Thereupon, the coating speed and the makeup of the coated film vary with time, so a monitoring system is necessary for feedback controlling.
Hence, how to provide a vacuum coating apparatus, that can perform various continuous vacuum coatings on the flexible substrate with modular designed chambers, that is capable of being arranged for different applications, of finishing the manufacturing process in a single run, so as to increase the yield effectively, lower the cost as well as enhance the product competitiveness, is an important subject.